Due to its characteristics of being easily applicable to various products and electrical characteristics such as a high energy density, a secondary battery is not only commonly applied to a portable device, but universally applied to an electric vehicle (EV) or a hybrid vehicle (HV), and an energy storage system that drive on an electric driving source. This secondary battery is gaining attention for its primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making it a new eco-friendly and energy efficient source of energy.
A battery pack used in the electric vehicle has a structure in which a plurality of cell assemblies is connected in series, each cell assembly including a plurality of unit cells, to obtain high output. Also, the unit cell can be charged and discharged repeatedly by electrochemical reactions between elements including a positive current collector, a negative current collector, a separator, an active material and an electrolyte solution.
In addition to this basic structure, the battery pack further includes a battery management unit (BMU) to monitor and control a state of a secondary battery by applying an algorithm for control of power supply to a driving load such as a motor, measurement of electrical characteristic values such as current and voltage, charge/discharge control, voltage equalization control, and estimation of a state of charge (SOC).
Recently, with the growing need for a high-capacity structure as well as utilization as an energy storage source, there is an increasing demand for a battery pack with a multi-module structure in which a plurality of battery modules including a plurality of batteries connected in series and/or in parallel are assembled.
Because the battery pack with a multi-module structure includes a plurality of batteries, there is a limitation in controlling the charge/discharge state of all the batteries using a single BMU. Accordingly, a recent technology has been introduced in which a BMU is mounted in each battery module included in the battery pack, one of the BMUs is designated as a mater BMU and the other BMUs are designated as a slave BMS, such that the charge and discharge of each battery module is controlled in a master-slave mode.
Japanese Patent Publication No. 2010-141971 discloses an example of earlier technology relating to the master-slave mode. The prior art discloses wherein a BMU designed to have a master status originally transmits a wakeup signal to a BMU designed to have a slave status originally.
However, earlier technology such as the above needs to make a double effort to produce a BMU having a master status and a BMU having a slave status separately and develop suitable algorithms for each status. Further, when an operation such as replacement/addition of an existing battery pack is required, setting an identifier in accordance with the status of the replaced/added BMU is complex.